I was thinking of just adding some out rigger type floats to the canoe, I saw a project in Wooden Boat magazine several years ago where a guy built two amas out of very thin plywood, built up some very cool curved akas out of 1/4" strips of 2x2 bent around a jig he'd made.

The whole thing attached to his canoe with clamps, so it was easy to remove...but then there's the sail issue...